A recombinant transfer vector, pBacIL-11, containing hIL-11 cDNA of 546 nucleotides lacking leader sequence was constructed and co-transfected into BmN cells with linearized BmBacPAK(modified BmNPV) DNA for construction of a recombinant baculovirus carrying the hIL-11 gene. Southern hybridization analysis suggested that the recombinant baculovirus DNA contained hIL-11 cDNA fragment. RNA dot blotting demonstrated that the hIL-11 gene was transcribed. The recombinant baculovirus has a strong infectivity to BmN cell line and to silkworm larvae and pupae. Specific hIL-11 bands were detected from all the samples of cell extract, culture supernatant, haemolymph of larvae and pupae by SDS-PAGE analysis. Biological activity of the expressed product was determined with IL-11 dependent B9-11 cell line and by MTT colorimetric assay, which indicated that biologically active rhIL-11 protein was overexpressed in BmN cell line and in silkworm larvae and pupae.